Copper base alloys upon prolonged exposure to air at room temperature develop non-uniform and unattractive oxide films commonly referred to as tarnish. To prevent such tarnishing, a variety of clear coatings have been developed that are either very costly or are subject to damage in use and resultant local tarnishing and corrosion under the coating. Thus, while the majority of copper base alloys possess the required formability for fashioning into useful articles, their lack of tarnish resistance limits their use in areas where these articles are also intended to serve a decorative function.
The search for a copper base alloy having a stainless property, that is, one which does not require a protective coating, has been active for many years. Indeed, the International Copper Research Association (INCRA) has developed an alloy of reasonable tarnish resistance that is known as INCRA C-57. This alloy consists of copper with 5 percent by weight tin and 7 percent by weight aluminum. However, this alloy is difficult to fabricate using conventional brass mill techniques. More specifically, this alloy does not hot roll very well and its cold rollability is also quite limited. In addition, the formability of the finished alloy is relatively low, severely limiting the application and utility of the alloy in the manufacture of formed articles. Thus, in order to gain the benefits of tarnish resistance in a copper base alloy, one has had to resort to compositions which possess inherently limited workability and formability. Primarily, for this reason such alloys have not gained widespread commercial acceptance.